The present invention relates to a movement detecting apparatus for detecting the degree of movement of images which are encoded and transmitted by means of a television signal.
As processing circuits for a television signal, there are known a noise reduction system using a frame-memory, an adaptive Y/C separator, a scanning sequence converter, as well as their circuits. One of the major problems to be solved in an apparatus of this type is to successfully detect the degree of movement of images which are represented by the television signal.
In the case of a monochromatic television signal, an interframe difference signal is generated by using a frame memory, and the degree of movement is detected based on the level of the interframe difference signal. On the other hand, in the case of a composite color television signal, one proposed method is to invert the polarity of a chrominance signal to match the phase of a color subcarrier in the NTSC system, and to generate an interframe difference signal which relates the degree of movement based on the level thereof. The above method is a suitable broad detection approach and it can be implemented with relatively simple hardware. But it is unsuccessful in detecting at the edge portion of an image. As an alternative, there is proposed a method by J. O. LIMB and J. A. MURPHY that is adapted to detect the velocity of moving images. This method is reported in "COMPUTER GRAPHICS AND IMAGE PROCESSING", April 1975, pp. 311-327, by the title of "Estimating the Velocity of Moving Images in Television Signals". According to the method, the speed S of moving images is determined by the following equation: ##EQU1## where FDS represents a frame difference signal, EDS represents a picture element difference signal and MA represents a moving area. With this method, the speed can be detected correctly and movement detection can be reliably performed at the edge portion of an image without error. However, the method is disadvantageous in that it necessarily requires more hardware when it is directly applied for processing a television signal in a real time base, because the moving area must be first detected and the total sum of the respective difference signals must be then calculated for the moving area in the real time.
In practice, it is not necessary to detect a direction of movement when the moving detection is applied to the adaptive Y/C separator, the scanning sequence converter or the like. Further, in such apparatus, it is also not necessary to precisely detect the speed of movement. When applying the moving detection to such apparatus, of importance is to know the approximate speed of moving area in the picture and not to erroneously interpret stationary image edges as a moving portion of the picture.